INTEGRATED CONTROL OF TROPICAL SIGNALGRASS (Urochloa subquadripara) IN TURF By DAVID PEARSAUL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2017 © 2017 David Pearsaul To my mom ACKNOWLEDGMENTS I would like to thank my major advisor, Dr. Ramon Leon, for giving me this opportunity and making this an enjoyable learning experience. I also thank my committee members, Dr. Maria Silveira, Dr. Brent Sellers, and Dr. Calvin Odero for their support and guidance throughout this process. I would also like to thank Ryan Duffell and Chuck Calhoun at Sandridge Golf Club and Christian Millican at Pointe West Country Club for being so accommodating over the past few years. I graciously thank Syngenta for their support, as this would not have been possible otherwise. Above all, I would like to thank my family, my wife Samantha for her unwavering support and our son Henry for motivating me above all else. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 6 LIST OF FIGURES .......................................................................................................... 7 ABSTRACT ..................................................................................................................... 8 CHAPTER 1 INTRODUCTION .................................................................................................... 10 Impact of Weeds ..................................................................................................... 10 MSMA Ban .............................................................................................................. 12 Weeds and Turf Quality .......................................................................................... 13 Integrated Weed Management ............................................................................... 14 Nonchemical Control ........................................................................................ 14 Chemical Control .............................................................................................. 15 2 AN INTEGRATED APPROACH TO TROPICAL SIGNALGRASS (Urochloa subquadripara) CONTROL IN TURF ...................................................................... 19 Summary ................................................................................................................ 19 Background ............................................................................................................. 20 Materials and Methods............................................................................................ 23 Results and Discussion........................................................................................... 25 IWM Study ........................................................................................................ 25 POST Study ..................................................................................................... 28 3 THE IMPACT OF SEEDLING RECRUITMENT ON TROPICAL SIGNALGRASS (Urochloa subquadripara) REESTABLISHMENT IN TURF .................................... 37 Summary ................................................................................................................ 37 Background ............................................................................................................. 37 Materials and Methods............................................................................................ 39 Results and Discussion........................................................................................... 40 4 SUMMARY AND CONCLUSIONS .......................................................................... 44 LIST OF REFERENCES ............................................................................................... 47 BIOGRAPHICAL SKETCH ............................................................................................ 51 5 LIST OF TABLES Table page 2-1 Herbicides, formulations, and rates used in the experiments ............................. 30 2-2 Effects of verticutting, preemergence (PRE) herbicide, and postemergence (POST) herbicide on tropical signalgrass (TSG) cover at 2, 4, 8, and 12 wk after initial treatment (WAIT) ............................................................................... 31 2-3 Interaction (P<0.0001) between preemergence (PRE) and postemergence (POST) herbicides on tropical signalgrass (TSG) cover at 52 wk after initial treatment (WAIT) ................................................................................................ 32 2-4 Postemergence (POST) tropical signalgrass (TSG) % visual cover and % of squares ot of 36 occupied by tropical signalgrass (% grid) at 2, 4, 8, and 12 wk after initial treatment (WAIT) for site 1 ........................................................... 33 2-5 Postemergence (POST) tropical signalgrass (TSG) % visual cover and % of squares ot of 36 occupied by tropical signalgrass (% grid) at 2, 4, 8, and 12 wk after initial treatment (WAIT) for site 2 ........................................................... 34 2-6 Synergism between amicarbazone and multiple mix partners at 2, 4, 8, and 12 wk after initial treatment (WAIT) .................................................................... 35 2-7 Turfgrass injury observed in postemergence (POST) herbicide study at 2, 4, and 8 wk after initial treatment (WAIT) ............................................................... 36 6 LIST OF FIGURES Figure page 3-1 Tropical signalgrass seedling emergence over time in the nontreated control and areas treated with S-metolachlor and indaziflam. Weeks after treatment (WAT). Error bars correspond to standard error of mean ................................... 42 7 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science INTEGRATED CONTROL OF TROPICAL SIGNALGRASS (Urochloa subquadripara) IN TURF By David Pearsaul December 2017 Chair: Ramon Leon Major: Agronomy Tropical signalgrass (TSG) has become a troublesome weed in south Florida following the removal of monosodium methane arsenate (MSMA), an effective and economical postemergence (POST) herbicide, from the turfgrass market at the end of 2012. Turfgrass managers have relied heavily upon this herbicide to control TSG, as well as many other weeds, for many years and are now searching for a comparable replacement. In an attempt to avoid a similar situation in the future, this thesis focuses on identifying an effective integrated weed management (IWM) strategy aimed at controlling TSG in bermudagrass turf. In one study, verticutting, a cultural practice that is regularly employed on many golf courses, was combined with preemergence (PRE) and POST herbicide treatments to determine whether TSG control would be increased using this integrated approach. The POST herbicides were then evaluated to determine the most efficacious combinations. Additionally, a PRE herbicide study was conducted to demonstrate the impact of seedling recruitment on TSG reestablishment. In this research, verticutting was found to provide limited weed control by itself. Amicarbazone demonstrated the ability to enhance other POST herbicides through 8 synergistic activity on TSG control with multiple modes of action. PRE herbicides proved to be a crucial component of a TSG management strategy, with indaziflam showing the greatest level of efficacy of those herbicides tested. 9 CHAPTER 1 INTRODUCTION Optimal turfgrass quality is the goal of many golf course superintendents and sod farm managers. Turfgrass managers constantly deal with both biotic and abiotic stressors while attempting to maintain ideal playing conditions or grow high-quality sod. Diseases, insects, and weeds are the most common biotic agents reducing turf quality and growth while water, nutrient deficiencies and temperature extremes are important abiotic stresses (Taiz et al. 2015). All sources of stress must be considered when implementing a turf management strategy. An unhealthy plant is more susceptible to injury from diseases or insects and, in the case of turfgrass, a thinned canopy can favor unwanted weed pressure ultimately eliminating the competitive advantage that the turfgrass may have had originally. This is similar to the agronomic cropping practice of increasing plant density and decreasing the spacing between rows in order to reduce the area and resources available to weeds (Buhler 2002). Impact of Weeds Weeds present an enormous challenge for agriculture, as well as turfgrass production and management, as evidenced by the estimated losses in corn and soybean yields in the absence of any control measures. Soltani et al. (2016, 2017) reported that approximately 50% of corn and soybean yields in North America (valued at $27 billion and $16 billion, respectively) would be lost annually by uncontrolled weeds. In 2012, the United States Environmental Protection Agency (USEPA) estimated the world market value for herbicides and plant growth regulators (PGR) to be approximately $25 billion, accounting for nearly half of all pesticide sales in the world (Atwood and Paisley-Jones 2017). Chemical control is the most heavily relied upon 10 method of pest